The brewing apparatuses commonly used at present in beverage vending machines normally comprise a brewing chamber movable between a first position, in which a brewing material can be loaded through an open end of the brewing chamber, and a second position, in which a first so-called pressure piston can be inserted inside the brewing chamber through its open end to compress the brewing material into a cake. A second so-called ejector piston, opposite the first piston and fitted with a filter, is located at the bottom of the brewing chamber, and slides inside the brewing chamber to eject the cake once brewing is completed.
A brewing apparatus of this type is described, for example, in EP 1 306 041, in which the second piston and movement of the brewing chamber are controlled by a disk with a cam on each face; and the first piston, which is only inserted inside the brewing chamber at the brewing stage, is controlled by a connecting rod-crank mechanism.
A drawback of this type of brewing apparatus, and all other similar types, in which the first piston is controlled by a connecting rod-crank mechanism, lies in the mechanism not only being bulky, particularly in the height direction of the apparatus, but also having a given bottom dead centre position which, if not reached, e.g. because of too much material inside the brewing chamber, prevents operation of the brewing apparatus.
In other words, known brewing apparatuses of this type have the major drawback of allowing no variation in the volume of the brewing chamber to brew different amounts of material, thus preventing use of a single brewing apparatus in vending machines producing different types of beverages.
Brewing apparatuses, such as the one described in EP 1 306 041, are also known which comprise a mechanism for positive control of both the oscillating movement of the brewing chamber and the up and down movement of the second piston; the term “positive control” being used here in the sense of a drive member controlling the movement of a driven member and all its physical parameters, such as speed, acceleration and trajectory.
Mechanisms of, this type, normally cam-controlled, are extremely complicated, by comprising one or more cam followers with members for transmitting motion to respective driven members. So much so that they may result in jamming and/or lack of coordination of the movements controlled by the mechanisms.